Liquid crystal on silicon (LCOS) has become a common technology in forming portable displays having high resolution. LCOS uses liquid crystal contained between a rear plate comprising silicon and a front transmissive plate. Reflective pixels are formed in an upper portion of the rear plate typically representing a third or higher order metallization layer above a silicon substrate. The lower metallization layers typically formed in dielectric insulating layers represent circuitry between electrical elements such as transistors and capacitors formed in the silicon substrate and the front plates including transparent electrodes (indium-tin-oxide electrode) to control a Voltage applied to the various pixel electrodes defining a portion of display cells of the LCOS display. The polarization of the light passing through the liquid crystal contained in the display cells is modulated altering the alignment of the liquid crystal molecules which correspond to an applied Voltage to the display cells.
In one approach to forming display cells a groove is formed between each pixel electrode and spacers, also referred to as pillars are formed over a portion of adjacent pixel electrodes to define a display cell containing the liquid crystal. The profile of the spacers and depth and width of the grooves is critical display performance. For example the alignment of the liquid crystal molecules which determines light transmission or reflection is determined is affected by the angle of inclination of the spacers, affecting brightness and contrast of the display. In addition, an electric fringe field effect at the pixel electrode edges, which also affects orientation of the liquid crystal molecules, is dependent on the etching profile of the grooves, an irregular etching profile reducing the brightness of the display.
A problem in prior art LCOS display manufacturing methods includes the etching process to form the spacers and the grooves making up portions of the display cells. For example spacers are formed by etching through a relatively thick layer of oxide, typically about 1 micron or greater, using a patterned photoresist layer. As a result, the photoresist layer thickness has been critical in prior art processes since a photoresist layer that is too thick will result in an unacceptable spacer sidewall profile and a photoresist layer that is too thin will result in etching damage to the spacer. Moreover, according to prior art LCOS spacer formation processes, in dry etching the groove between pixel electrodes, the formation of metal containing polymeric etching residues frequently causes premature etch stop as the steady state build up of etching residues equal or exceeds material removal, resulting in grooves having undesirable profiles and depths.
There is therefore a need in the LCOS display manufacturing art to develop a manufacturing process whereby spacers and pixel edge grooves may be formed reliably with improved etching profiles to improve display performance including improving LCOS display brightness and contrast.
It is therefore among the objects of the present invention to provide a manufacturing process whereby spacers and pixel edge grooves may be formed reliably with improved etching profiles to improve display performance including improving LCOS display brightness and contrast, while overcoming other shortcomings of the prior art.